Press Release:

This artist's conception shows the inner four planets of the Gliese 581 system and their host star, a red dwarf star only 20 light-years away from Earth. The large planet in the foreground is the newly discovered GJ 581g, an Earth-size planet that orbits in the star's habitable zone. Artwork by Lynette Cook.

The planet, which is probably 30 percent larger than Earth, was discovered using one of the telescopes of the W. M. Keck Observatory on Mauna Kea. It orbits a relatively small star, Gliese 581, that is 20 light-years from Earth in the constellation Libra.

“By determining the orbit of this planet, we can deduce that its surface temperature is similar to that of Earth,” said Haghighipour. This means that at least some of any water on the surface of the planet and in its atmosphere will be in liquid form rather than ice or vapor. The discovery of liquid water in space is an important step in the search for extraterrestrial life.

The team estimates that the new planet, called Gliese 581g, has a mass three to four times that of Earth, and orbits its star in just under 37 Earth days. Its mass indicates that it is probably a rocky planet with enough gravity to hold on to its atmosphere. It is one of six known planets orbiting the star.

To discover the planet, the team looked for the tiny changes in the star’s velocity that arise from the gravitational tugs of its planets. They used 238 separate observations of Gliese 581 taken over a period of 11 years.

Haghighipour said that the team is keeping tabs on many nearby stars using the Keck Observatory. “As we collect more and more data about how these stars are moving, we expect to find many more planets with potentially Earth-like conditions,” he said. He noted that to learn more about the conditions on these planets would take even bigger telescopes, such at the Thirty Meter Telescope planned for Mauna Kea.

The team that made the discovery is led by Steven Vogt of the University of California, Santa Cruz (UCSC) and Paul Butler of the Carnegie Institution of Washington. Other team members include UCSC associate research scientist Eugenio Rivera, and Gregory Henry and Michael Williamson of Tennessee State University.

This research was supported by grants from the National Science Foundation, NASA, and the NASA Astrobiology Institute.